1. Field of the Invention
The present invention relates to an electric actuator and, more particularly, to an electric actuator equipped with a retractable plunger that can protrude from and retract into the body of the actuator.
2. Description of the Related Art
As is generally the case, the conventional motorized vehicle 100, as shown in FIG. 1, has a door 101 equipped with a locking device 102. This locking device 102 locks the door 101 in a closed position. A door handle 103, attached to the inner panel of the door 101, allows the vehicle's operator to both open and lock the door 101 by disengaging and engaging the locking device 102. It is also generally the case that the locking device 102 comes equipped with a locking mechanism to prevent the locking device 102 from being operated despite the operation of the door handle 103. A knob 106, connected to the locking mechanism by a lever 105, allows the vehicle's operator to engage or disengage the locking mechanism. When the knob 106 is pulled up or down, the locking mechanism in the locking device 102 can be operated through the lever 105. When the knob 106 is lowered, the locking device 102 engages the locking mechanism in a locked state to prevent the door from opening even if the door handle 103 is manipulated. When the knob 106 is raised from a lowered position, the locking mechanism is disengaging allowing the door to be opened by operation of the door handle 103.
An electric actuator 107 is incorporated inside the door 101, and connects to the locking device 102 via the lever 105. As shown in FIG. 2, the electric actuator 107 is coupled to a safe lock switch 109 and a vehicle speed sensor 110 via an electric control unit (i.e., ECU) 108 provided with the vehicle 100. The safe lock switch 109, disposed in the door 101, and the vehicle speed sensor 110 are electrically coupled with the locking device 102.
When the vehicle 100 is operated at a predetermined speed with unlocked doors (i.e., in the unlock state of the locking device 102), the ECU 108 operates the electric actuator 107 in response to a signal generated by the vehicle speed sensor 110. In such a case, the electric actuator 107 causes knob 106 to be placed in a lowered or depressed position. The actuator 107 thus causes the locking mechanism to secure the door 101 in a locked state. In other words, the electric actuator 107 pulls down the knob 106 and actuates the locking mechanism in the locking device 102 through the lever 105. Thus, the locking device 102 comes into the lock state in which the door 101 cannot be opened even if the door handle 103 is operated.
When the safe lock switch 109 is operated by a vehicle's operator, with the device 102 in the lock state, for the purpose of opening the door, the ECU 108 operates the electric actuator 107 to pull up the knob 106 and brings the locking device 102 into the unlock state, in which the door 101 can be opened if the door handle 103 is operated. On the other hand, when the safe lock switch 109 is operated by the vehicle's operator with the device 102 in the unlock state, the ECU 108 operates the electric actuator 107 and actuates the locking mechanism in the locking device 102 through the lever 105. Thus, the locking mechanism is forcibly operated independently of the vehicle speed to establish the lock state, in which the door 100 cannot be opened even if the door handle 103 is operated.
In addition to the above operation, the locking mechanism can also be manually operated by a vehicle passenger by physically manipulating the knob 106 up or down to respectively lock or unlock the door 101 (i.e., to bring the locking mechanism into the lock state or unlock state).
An Examined Japanese Patent Publication No. 3-25590 discloses a traditional electric actuator for switching the locking device 102 between the lock state and unlock state. This electric actuator comprises a rotary disc having a cam groove and a cam follower lever provided with a cylindrical cam follower. As the rotary disc is rotated clockwise by a drive motor, the cam follower slides along the cam groove of the rotary disc. When the cam follower comes into contact with a first abutting portion formed in the cam groove to define a locking position, the rotation of the rotary disc is regulated. Then, the cam follower lever operates the locking device to bring the door into the lock state. On the other hand, when the rotary disc is rotated counter-clockwise, this causes the cam follower to contact with a second abutting portion formed in the cam groove to define an unlocking position. Consequently, its rotation is regulated, and the cam follower lever operates the locking device to bring the door into the unlock state.
The cam follower lever in the conventional actuator, however, utilizes only one cam follower. Each time the single cam follower slides along the cam groove, it comes into collision against the inner walls of the cam groove at the first and second abutting portions. In addition, the cam follower is always in sliding contact with the cam groove. As a result, the cam follower is subject to being seriously worn.
Moreover, since the cam follower is formed with a cylindrical shape, the abutment between the follower and the first or second abutting portions in the cam groove results in line-contact. As a result, an impact is always applied to specific portions of the cam follower, lowering the durability of the cam follower. These types of actuators also require relatively large numbers of component parts. This makes their manufacture and assembly relatively complex and difficult.
In the conventional actuator, moreover, a force may be applied to an engaging projection of a lock lever through a fork member connected to the knob, when the actuator is manually operated. At this time, the cam follower lever is turned by an intermediate lever connecting the cam follower lever with a lock lever. As the cam follower lever is turned, the cam follower linearly moves along a linear groove joining the first abutting portion with the second abutting portion. Unless the cam follower is disposed in the linear joining groove, however, the locking device cannot be manually operated in response to the manual operation of the knob.